Electron orbiting device including a flat,ribbon-type,thermionic filament



I June 11, 1968 R. G. HERB ET Al- ELECTRON ORBITING DEVICE INCLUDING A FLAT, RIBBON-TYPE, THERMIONIC FILAMENT Filed April 15, 1965 5 Dn mom N @NBN mw/wu s @am NH a EG. P V w d E v l m f mw y a s. w m, l ww w.. W m. A|u| m www m ,MJ H w@ Q n m QG w ||..l N L QN@ Q@ -mma W m e l| NdT/Iv Y NS Sud m. #Qn .r Qms Whw {.vow w L' s .h N n H 3 l v m NQ QWJWI @v @v United States Patent O 970,93 11 Claims. (Cl. 315-108) ABSTRACT 0F THE DISCLOSURE An electron orbiting device for use as an ion-getter vacuum pump, ion gauge, electrometer tube, amplifying device or the like, comprising a cylindrical anode rod or wire, a cylindrical boundary electrode concentric with said anode, means for applying a positive voltage to said anode relative to said boundary electrode to produce a radial electric field therebetween, and an electron emitting electrode disposed between said anode and said boundary electrode toward one end thereof and at a potential approximately the same as that of the boundary electrode or slightly positive relative thereto, said electron emitting electrode preferably being in the form of a flat ribbon and having a flat electron emitting surface in a radial plane and disposed edgewise toward said anode so that the electrons emitted by said surface will be given substantial angular momentum about said anode whereby the electrons will Ibe introduced into orbits around said anode.

This invention relates to electron orbiting devices and pertains particularly to devices which have important applications to ion gauges, electrometer tubes, amplifying devices and ion-getter vacuum pumps.

The electron orbiting device of the present invention is 4of the general type disclosed and claimed in our copending application Ser. No. 332,190, now Patent No. 3,244,969, filed Dec. 20, 1963, which is a continuationin-part of our application Ser. No. 261,104, now Patent No. 3,244,990, filed Feb. 26, 1963. The present application corresponds to French patent application Ser. No. 970,934, filed Apr. 15, 1964, particularly FIGS. 17, 18 and 19 thereof and the corresponding description. The priority of the French application is claimed under the International Convention in support of the present application.

One object of the present invention is to provide an electronic device of the foregoing character in which the electrons are injected into the device in a new and improved manner so that the mean free path of tue electrons will be much longer than the over-all size of the device, so that the probability that any electron Iwill ionize a gas molecule in the device is greatly increased, the device thereby being adapted to. serve as a highly efficient ion gauge, or as an ion-getter vacuum pump. f A further object is to provide a new and improved electronic device of the foregoing character in which the mean free path of the electrons is increased by injecting the electrons in a new and improved mann-er so as to cause them to travel in spiral paths or orbits, around one of the electrodes of the device, without utilizing any magnetic field.

It is a further object'to provide an electron orbiting device of the foregoing character in which the electrons are injected in a new and improved manner. so as to travel in spiral orbits and in an electric field between an outer cylindrical electrode and an axial electrode in the form of a wire or cylinder received within the outer electrode.

Another object is to provide such an electron orbiting device in which the electrons are injected or introduced ice in a new and improved manner into the space between the inner and outer electrodes with a substantial angular momentum so that the electrons will travel in spiral orbits around the inner electrode.

A further object is to provide such an electron orbiting device in which the electrons are injected in a new and improved manner by a heated electron emitting ribbon filament disposed between the inner and outer electrodes and generally parallel to the inner electrode.

Another object is to provide such a new and improved electron -orbiting device in which the ribbon filament is disposed substantially in a radial plane which includes the inner electrode, so that the electrons will be emitted from the flat sides of the ribbon filament with substantial angular momentum about the inner electrode.

A further object is to provide such a new and improved electron orbiling device in which the ribbon filament is doubled Iback to form a generally U-shaped loop having two closely-spaced parallel legs which are disposed so that the electrons are emitted from the flat outer sides of the legs with high angular momentum about the inner or central electrode.

Further objects and advantages of the present invention will appear from lthe following description, taken with the accompanying drawings, in which:

FIG. 1 is a diagrammatic longitudinal section showing an ion-getter vacuum pump to be described as an illustrative embodiment of the present invention.

FIG. 2 is an enlarged edge -view of one of the ribbon filaments employed in the pump of FIG. 1, the view being taken generally along the line 2-2 in FIG. l.

FIG. 3 is an enlarged side view of one of the ribbon filaments, taken generally as indicated by the line 3 3 in FIG. 2.

It will be seen that FIG. 1 illustrates an electron orbiting device in the form of an ion-getter vacuum pump 780. However, it will Ibe realized that the invention is applicable to other suitable electron orbiting devices in which electrons are caused to travel in spiral orbits in an electric field. Thus, for example, the present invention is applicable to ion gauges, eleetrometer tubes and other similar devices in which the electrons are orbited in an electric field around the inner electrode of the,device.

The getter ion pump 700y of FIG. 1 comprises a cylindrical metal casing 602, closed at one end by a plate or end wall 604. The other end of the casing 602 has an opening 606 which is adapted to be connected to the vacuum system 607 with which the pump is to be used. Thus, the pumping is done through the open end 606 of the casing 602. In this case, the end wall 604 is at the upper end of the casing `602.

The pump 780 is provided with a central electrode in the form of a cylindrical rod or wire 610. Normally, the rod 610 is positioned axially within the casing 602. The upper end portion of the rod 610 is supported by an insulator 612 which is sealed around the rod 610 and is sealed into an opening 614 in the upper end plate 604, whereby the upper end of the rod 610 is brought out of the casing 602 so that an electrical connection may be made to the rod.

A cylindrical terminating electrode or sleeve 616 is preferably mounted around the upper end portion of the `axial rod `610, just below the insulator `612. It will be understood that the axial rod 610 is insulated from the terminating electrode 616. The illustrated terminating e-lectrode 616 is coaxial with the axial rod 610 and is spaced rather closely thereto. Thus, the diameter of the terminating electrode 616 is considerably `smaller than the inside diameter of the cylindrical casing 4602. The terminating electrode is normally maintained .at lthe same or approximately the same potential as the outer casing 3. 602. As shown, the terminating electrode 616 is connected to the casing 602.

A 1direct current power supply 620 is employed to provide a high positive voltage between the central rod 610 and the cylindrical casing 602. For example, such voltage may be about 5,000 volts.

Means are provided for introducing or injecting electrons into the space between the casing 602 and the central rod 610, in such a manner that the electrons will go into orbits in the electric field around the central rod. Thus, the pump employs electron injecting devices 782, each of which takes the form of a ribbon filament 784. Each filament 784 emits electrons which go into orbits around the inner or central electrode 610. The filaments 784 are electrically heated preferably by current derived from the secondary winding 410 of a transformer 408. The ends of each fila-ment 784 are mounted on terminal leads 786 and 788 which are connected -across the secondary winding 410.

Each ribbon filament 784 is positioned with its flat surfaces extending along planes which are generally radial with respect to the inner electrode 610. Thus, the electrons emitted by the flat outer surfaces of the ribbon filiment 784 are given initial impetus in directions generally at right angles to the radial direction. Accordingly, a high percentage of the electrons acquire sufficient angular momentum to cause them to go into orbits around the inner electrode 610.

Each of the illustrated ribbon filaments 784 is folded or doubled to form a narrow elongated U-shaped loop having two legs 790 and 792 which are closely spaced and generally parallel to each other. The free ends of the legs 790 and 792 are connected to the terminal leads 796 and 798.

Successful tests have been made with a ribbon filament in the form of rhcnium foil about one-sixteenth of an inch wide and with folded legs about one-thirty-second of an inch apart. It will be understood, however, that the dimensions of the filament may be varied over a wide range to suit various conditions.

In addition to the low voltage secondary winding 410, the transformer 408 has a primary winding 412 which may be connected to a conventional source of alternating current, represented by line wires 413 yan-d 414.

Preferably, the ribbon filaments 784 `are biased .to a positive potential with respect to the outer casing 602, so as to prevent the emitted electrons from travelling to the outer casing. The biasing voltage may be provided by a battery 416, or some other source of direct current. As shown, `a potentiometer 417 is connected across the battery 416 to adjust the biasing voltage. The movable contact 416 of the potentiometer 417 is connected to a center tap 419 on the secondary winding 410. The negative terminal of the battery 416 is connected to the casing 602.

To provide for the evaporation of gettering material, a slug or target 624 of gettering material is mounted on the central rod `610, near the lower end of the rod but spaced upwardly a substantial distance therefrom. Thus, the central rod 610 has a portion 626 which projects below the slug or target 624. As shown, the lower end portion 626 of the rod 610 terminates .a substantial distance above the lower end of the casing 602. Preferably, the extreme lower end of the lower end portion 626 is free and unsupported by any insulator or the like.

The target or slug 624 may be made of titanium, or some other getter material, and may be cylindrical in form. It is preferred that the rod `610 be made of tungsten or some other material which will withstand high operating temperatures.

A sensitive meter 794 is connected between the casing 602 `and the direct current power supply `620 to measure the ion current to the casing 602. Such current gives :an indication of the pressure which exists in the casing 602 of the vacuum pump during normal operation.

To prepare the pump 780 for normal operation, the space within the casing 602 and the vacuum system 607 is evacuated to a fairly low lpressure -by the use of any conventional or lsuit-able fore pump. Energizing voltages are then applied to the getter ion pump 780. Over a fairly short period of time the getter ion pump 780 `reduces the pressure in the casing 602 and the vacuum'system 607 to a very low level, much lower than can be achieved with a fore pump or most other types of vacuum pumps.

During the normal operation of the getter ion pump 780, the ribbon filaments 784 are heated electrically to a temperature at which they emit electrons.

Most of the electrons are emitted by the flat outer surfaces of the ribbon filaments 784. Such electrons are emitted with substantial components of velocity at right angles to the radial electric field between the central rod 610 and the outer cylindrical casing 602. Accordingly, `such electrons are injected into the electric field with substantial angular momentum about the central rod 610. The angular momentum causes the electrons to go into spiral orbits in the electric field around the central rod 610. The orbiting electrons spiral downwardly around the rod 610. Many of the orbiting electrons will at first miss the titanium target or slug 624 and will continue to spiral downwardly around the slug 624 and around the lower end portion 626 of the central rod 610. Most of the electrons which spiral to the lower end of the lower rod portion 626 are reflected upwardly by the electric field between the free lower end of the lower rod portion 626 and the casing 602. The reflected electrons continue to orbit around the lower rod portion 626 but will spiral upwardly. Again, many of the spiraling electrons will miss the titanium slug 624 and will travel in orbits around the slug and around the upper portion of the central rod 610. The strong electr-ic field between the terminating electrode or sleeve 616 and the central rod 610 causes most of the upwardly spiraling electrons to be reflected downwardly so that they will travel downwardly in spiral orbits around the rod 610. Thus, the orbiting electrons may spiral several times along the length of the central rod 610. In this way, the mean free path of the electrons is lengthened so that there will be an increased probability that each `electron will encounter a gas molecule so as to ionize the molecule. Thus, the number of gas ions produced by the electrons is increased.

Some of the orbiting electrons pass so close to the central rod 610 that they strike the titanium slug 624, either on the first pass along the central rod, or on subsequent passes, after the orbits of the electrons have been modifed, by reflection at the ends of the central rod, by collision with gas molecules, or by other disturbing factors. Eventually, the titanium slug or target 624 intercepts many or most of the orbiting electrons. The resulting electron bombardment of the titanium slug 624 causes heating of the slug, so that the titanium is evaporated from the slug. Normally, the temperature of the slug is kept below the melting point of titanium, so that titanium is evaporated by sublimation, directly from the solid state to the vapor state. The orbiting electrons strike the titanium slug 624 at various places along the slug, so that the slug is heated in a fairly uniform manner along its entire length.

The titanium vapor travels outwardly from the target or slug 624 and is condensed on the inner surface of the casing 602. The freshly condensed or deposited titanium takes up and buries gas molecules and ions. The orbiting electrons cause substantial ionization of the gas molecules in the space around the central rod 610. The positive gas ions are propelled to the outer casing 602 by the electric field between the casing and the central rod 610. When the ions strike the casing 602, they tend to be buried by the continuously deposited titanium getter. The efficient ionization of the gas molecules is particularly important in obtaining high pumping rates for the noble gases, such as argon and helium.

The getter ion pump illustrated in FIG. 1 will achieve a high pumping rate, both for air and for the noble gases, such as argon. The pump is capable of reducing the pressure in the vacuum system to extremely low levels.

The ribbon filaments 784 inject the electrons into orbits around the central electrode 610 with a high degree of efficiency. Moreover, the ribbon fialments are capable of providing high emission of electrons. It will be understood that a single ribbon filament may be employed, if desired. In that case, the other ribbon filament may be omitted or may be disconnected from the filament transformer so that it may be used later as Ia spare. The use of two filaments provides an electron emission current which is twice the current obtainable with a single filament. lf still greater emission of electrons is desired, three or more filaments may be employed. Normally, the filaments are spaced at equal angular intervals around the central rod 610.

The ribbon filaments are strong and durable s-o that they provide long operating life. The ribbon filaments have the additional advantage of being easy to make up from metal foil.

It will be -appreciated that the ribbon filament is one form of an electron emitting electrode having a substantially flat electron emitting surface which is oriented so as to emit electrons with lsub-stantial angular momentum about the central or axial electrode. Other electron emitting electrodes of this general character may be employed, such as electron emitting sheets, plates or the like. Generally, the fi-at electron emitting surface is disposed edgewise toward the central electrode so that the electr-ons emitted from the fiat surface will be given a substantial angular momentum about the central electrode. Thermionic emission of electrons is preferred, but photoelectric emission may also be employed in some cases. The edgewise disposition of the electron emitting electrode minimizes the number of electrons which proceed directly to the inner electrode without going into orbits. With a favorable disposition of the at electron emitting electrode, -a high percentage of the electrons emitted from the fiat surface or surfaces have sufficient angular momentum to go into orbits about the central electrode.

Various other modifications, alternative constructions and equivalents may be employed without departing from the true spirit and scope of the invention, as exemplified irlr the foregoing description and defined in the following c aims.

We claim:

1. An electronic device,

comprising an elongated inner electrode which is generally circular in cross section,

a boundary electrode extending around said inner electrode and spaced outwardly therefrom,

means for applying a voltage between said inner electrode and said boundary electrode such that said inner electr-ode is at a positive potential relative to said boundary electrode,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes,

said electron emitting electrode comprising a thermionic filament in the form of a fiat ribbon which is generally in a longitudinal radial plane with respect to said inner elect-rode, said device having a clear space between said filament and said inner electrode.

`2. An electronic device,

comprising an elongated inner electrode which is generally circular in cross section,

a boundary electrode extending around said inner electrode and spaced outwardly therefrom,

means for applying a voltage between said inner electrode and said boundary electrode such that said inner electrode is at a positive potential relative to said boundary electrode,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes,

said electron emitting electrode comprising a thermionic filament in the form of a fiat ribbon,

which is generally parallel to said inner electrode and is generally in a radial plane with respect thereto, said device having a clear unobstructed space between said filament and said inner electrode.

3. An electronic device,

comprising an elongated inner electrode which is generally circular in cross section,

a boundary electrode extending around said inner electrode and spaced outwardly therefrom,

means for applying a voltage between said inner electrode and said boundary electrode such that said inner electrode is at a positive potential relative to said boundary electrode,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes,

said electron emitting electrode comprising a thermionic filament in the form of a fiat ribbon,

which is disposed generally edgewise toward said inner electrode and generally in the axial plane thereof.

4. An electronic device,

comprising an elongated inner electrode which is generally circular in cross section,

a. boundary electrode extending around said inner electrode and spaced outwardly therefrom,

means for applying a voltage between said inner electrode and said boundary electrode such that said inner electrode is at a positive potential relative to said boundary electrode,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes,

lsaid electron emittiing electrode comprising a thermionic filament in the form of a fiat ribbon,

said ribbon being folded double to form a loop with a pair of closely-spaced legs disposed generally edgewise towa-rd said inner electrode and generally parallel to a longitudinal radial plane therethrough.

5. An electronic device for use in a vacuum system,

said device comprising an elongated generally cylindrical inner electrode,

a generally cylindrical boundary electrode extending aronud and spaced outwardly from said inner electrode,

means for applying to said inner electrode a positive potential relative to said boundary electrode to produce a generally radial electric field therebetween,

and an electron emitting electrode disposed in the Ispace between said inner and boundary electrodes for introducing electrons into orbits in said electric eld around said inner electrode,

said electron emitting electrode having a substantially fiat electron emitting surface disposed generally edgewise to said inner electrode and generally paral lel to the electric field between said inner and boundary electrodes so that substantial angular momentum about said inner electrode is imparted to the electrons emitted by said fiat surface.

6. An electronic device for use in a vacuum system,

said device comprising an elongated generally cylindrical inner electrode,

a generally cylindrical boundary electrode extending around and spaced outwardly from said inner electrode,

means for applying to said inner electrode a positive potential relative to said boundary electrode to produce a generally radial electric field therebetween,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes for introducing electrons into orbits in said electric field around said inner electrode,

said electron emitting electrode having a substantially fiat surface disposed in said electric field generally parallel thereto and generally edgewise toward said inner electrode to emit electrons with substantial angular momentum about said inner electrode, said device having a substantially clear space between said electron emitting surface and said inner electrode.

7. An electronic device for use in a vacuum system,

said device comprising an elongated generally cylindrical inner electrode,

a generally cylindrical boundary electrode extending around and spaced outwardly from said inner electrode,

means for applying to said inner electrode a positive potential relative to said boundary electrode to produce a generally radial electric field therebetween,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes for introducing electrons into orbits in said electric field around said inner electrode,

said electron emitting electrode comprising a at thermionic sheet member having a at electron emitting surface generally edgewise to said inner electrode and generally parallel to the electric field between said inner and boundary electrodes for emitting electrons with substantial angular momentum about said inner electrode, said device having a substantially clear space between said electron emitting sur- -face and said inner electrode.

8. An electronic device for use in a vacuum system,

said device comprising an elongated generally cylindrical inner electrode,

a generally cylindrical boundary electrode extending around and spaced outwardly from said inner electrode,

means for applying to said inner electrode a positive potential relative to said boundary electrode to produce a generally radial electric field therebetween,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes for introducing electrons into orbits in said electric field around said inner electrode,

said electron emitting electrode comprising a thermionic filament in the form of a flat ribbon disposed generally edgewise toward said inner electrode and `generally in a longitudinal radial plane therethrough to emit electrons with substantial angular momentum about said inner electrode.

9. An electronic device for use in a Vacuum system,

said device comprising an elongated generally cylindrical inner electrode,

a generally cylindrical boundary electrode extending around and spaced outwardly from said inner electrode,

means for applying to said inner electrode a positive potential relative to said boundary electrode to produce a generally radial electric eld therebetween,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes for introducing electrons into orbits in said electric ield around said inner electrode,

said electron emitting electrode comprising a thermionic filament in the form of a flat iibbon which is folded double to form a loop with closely-spaced legs,

said ribbon being disposed generally edgewise toward said inner electrode and generally parallel to a longitudinal radial plane therethrough to emit electrons with substantial angular momentum about said inner electrode.

10. An electronic device,

comprising an elongated inner electrode which is generally circular in cross section,

a boundary electrode extending around said inner electrode and spaced outwardly therefrom,

means for applying a voltage between said inner electrode and said boundary electrode such that said inner electrode is at a positive potential relative to said boundary electrode,

and an electron emittingelectrode disposed in the space between said inner and boundary electrodes,

said electron emitting electrode having a at electron emitting surface disposed generally edgewise toward said inner electrode and generally in a longitudinal radial plane therethrough to emit electrons with substantial angular momentum about said inner electrode.

11. An electronic device,

comprising an elongated inner electrode which is generally circular in cross section,

a boundary electrode extending around said inner electrode and spaced outwardly therefrom,

means for applying a voltage between said inner electrode and said boundary electrode such that said inner electrode is at a positive potential relative to said boundary electrode,

and an electron emitting electrode disposed in the space between said inner and boundary electrodes,

said electron emitting electrode comprising a thermionic sheet member disposed generally edgewise toward said inner electrode and generally in a longitudinal radial plane therethrough for emitting the electrons with substantial angular momentum about said inner electrode, said device having a substantially clear space between said thermionic sheet member and said inner electrode.

References Cited UNITED STATES PATENTS 1/1967 Gabor 313-7 6/1932 Hull 313--264 X 3/1966 Laierty 313-7 X 4/1966 Herb et al 313--7 X JAMES W. LAWRENCE, Primary Examiner.

P. C. DEMEO, Assistant Examiner. 

